Author Topic: Back to 240V  (Read 23880 times)

buickanddeere

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Re: Back to 240V
« Reply #15 on: May 19, 2015, 08:43:06 AM »


Both 240 plugs in the back of the generator are three conductor.

Two live lines and a ground, no neutral ?

dieselgman

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Re: Back to 240V
« Reply #16 on: May 19, 2015, 09:42:04 AM »
In some systems the neutral is also bonded to ground... winds up being electrically the same thing.

dieselgman
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buickanddeere

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Re: Back to 240V
« Reply #17 on: May 22, 2015, 08:15:04 PM »
In some systems the neutral is also bonded to ground... winds up being electrically the same thing.

dieselgman

Not a good idea nor is it sound electrical theory.
Why is there an insulated white load current carrying conductor AND a bare ground wire that is supposed to bond equipment to near earth potential?
   Why is there two insulated wires and a bare ground wire inside a piece of NMD-7 house wiring?
« Last Edit: May 24, 2015, 02:43:19 AM by buickanddeere »

dieselgman

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Re: Back to 240V
« Reply #18 on: May 22, 2015, 10:00:16 PM »
Quote
In some systems the neutral is also bonded to ground... winds up being electrically the same thing.

I apologize for that sloppy and incomplete statement!  :-[ I now see that it could easily be misunderstood. A necessary clarification here... any neutral to ground bonding will take place at the source distribution panel or service entrance only! Never out at any receptacles or equipment connection boxes.

It is because you must never use the ground wire as one of your live conductors within your house (or equipment) wiring. The ground is there as a safety conductor only for the possibility of equipment or wiring short circuits. This ensures that the circuit breaker (or fuse) will interrupt the circuit at its source if a short or insulation failure occurs anywhere in the circuit. This does NOT mean that the neutral or white insulated conductor in the circuit is not common with the ground in the system. Ultimately it will be as previously stated except for the clarification about physical circuit design and that bonding must be at the source fuse or circuit breaker (service entrance only) in most cases. Electrical code requirements may have flip-flopped over time but at one time a neutral bonded to ground (in the distribution panel) was a standard requirement... the manufacturers do provide for this option within their breaker or fuse panels - standard. North America NEC. We bond neutral to ground in many of our genset wiring configurations - and also provide a solid grounding rod connection from earth to all chassis portions of the plants. Some exceptions do exist but this is the norm. Take another look at the schematic diagram in one of the prior posts... Neutral is common with earth ground.

For operator and personnel safety there can NEVER be an electrically live chassis or metal casing or conduit located anywhere in the system even if accidental or caused by insulation failure. Add to this the potential exposure to electrical discharge in the event of lightning strikes. The ground portion of the circuit is therefore of very high priority.

It is of significant importance that you always have your electrical system at least vetted and safety checked by a professional who knows your local code requirements. Electrical shock can easily be lethal and must never be treated as something of only a casual or passing concern.


Proper grounding and neutral bonding can be a complex and convoluted topic... the finer details are outside the scope of my discussion here. See NEC...

Where is it NEC compliant to bond neutral and ground? The NEC prescribes two places. The first place that we find this bond is at the service entrance inside the main service panels. Why? Fault current at this point needs to come from the utility source.
The other place where the neutral and ground are required to be bonded is on the secondary side of what the NEC calls a "separately derived system." The most common separately derived system is a power transformer where the primary and secondary windings are galvanically isolated from one another. This describes the NEMA-type transformer widely used to distribute power inside all commercial buildings. The reason for this is simple safety. The NEC wants the transformer providing the electric current in its own distribution system
to be sole source for fault current in the event of a fault in that distribution system. Fault current that does not have a short, low impedance path will not open breakers immediately.


Our generators are technically treated as separate utility "sources" but when connected through a transfer switch with household wiring and grid utilities it is sometimes important to also switch the neutral to avoid a code violation caused by the Neutral/Ground bond that is commonly present in the generator itself. Not all transfer switch types have this specific feature and not all localities will enforce this rule in the exact same way.

dieselgman
« Last Edit: May 23, 2015, 05:21:11 AM by dieselgman »
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BruceM

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Re: Back to 240V
« Reply #19 on: May 23, 2015, 05:41:34 AM »
I recently modified a portable 4KW 120V Sportsman brand propane generator set to provide either 120V or 240V via a 4PDT switch.
It also had a 2 pole generator head.  It is pretty often easy to switch the wiring from the head either way.  With the two poles windings in series you get 240 and a neutral. With both windings in parallel, 120V.  If you follow the wires back from the outlets, they will lead to the windings, and usually you can then get it sorted out. 






ottawavalleyboy

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Re: Back to 240V
« Reply #20 on: October 16, 2015, 10:07:40 PM »
I will not vouch for that transformer being the best overall solution, (I have never had to use such a modification for a simple single-phase power supply)... but it should work fine if kept within its voltage and specified load specs.

US 240ac is sometimes referred to as split-phase because it uses a center-tapped transformer from the supply (single-phase). 240vac IS 240vac regardless. Take a look at the discussions on this forum and do a quick web search for split-phase AC.

Perhaps this diagram will help clarify: EU vs US supply transformers are going to be different in how they are tapped for a specific voltage range. Line voltage (as well as frequency) is different.



dieselgman
I am planning on setting my St5 to backfeed the 240 volt appliance outlet of my cottage so I can operate select 120 volt circuits,
being careful not to forget disconnecting the building from the grid of course....but noticed that when reading other posts on this
matter that pulling 120v (v1,v2) individually from the generator wired in this manner cuts the available amps by half.

So my question is ....When I pull 240 volts from v1+v2  does the same amperage restriction apply?
A newbie question maybe but I did search the forums diligently....
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Tom

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Re: Back to 240V
« Reply #21 on: October 16, 2015, 11:01:44 PM »
No, you can pull 1/2 the amps from each leg.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

ottawavalleyboy

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Re: Back to 240V
« Reply #22 on: October 17, 2015, 08:29:50 PM »
Ok, thanks Tom...so I have an ST 5 wired for 240 V and that would be 10.5 amps from one leg and 10.5 amps from the other, correct?
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carlb23

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Re: Back to 240V
« Reply #23 on: October 17, 2015, 09:36:22 PM »
You should be able to pull around 20 amps per leg @ 120 each for 4800 watts max.

Tom

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Re: Back to 240V
« Reply #24 on: October 18, 2015, 12:12:09 AM »
Yes, however its best to load each leg evenly. If you just can't do that a balancing transformer will help. I use one in my setup.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

buickanddeere

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Re: Back to 240V
« Reply #25 on: June 07, 2016, 02:47:20 PM »


Thanks for the reply, I'll pass this on to my electrician/friend who is helping me get things changed around. My main concern now is weather the transformer I ordered, and will most likely arrive today, will work or catch fire and blow up when I try and use it. I was told the European 240 was not the same as in the US, so if this transformer .."Simran THG-3000 Step Down Voltage Transformer 3000 Watts Converts AC 220 / 240 Volt to 110 Volt"  will indeed not work I can send it back with the UPS driver and avoid a catastrophic indecent and likely divorce.  This is what my neighbor had to say about that transformer......   Does it sound correct?

 "The clue is in the words: " Converts single phase 220/240 V to 110/120 V".  It is a simple step down transformer.
 
The 220 we have in the US is NOT single phase. The 220 volts we have is for loads connected BETWEEN  the two 110 volt lines (each out of phase with the other).  "


120/240 is single phase with the load connected between two current carrying conductors. Three phase power is loads using three current carrying conductors and a 120 degree phase shift.